The present invention generally relates to a vane backpressure providing apparatus for a sliding vane type compressor.
Generally, in the sliding vane type compressor, construction is widely used that the high-pressure lubricating oil is adapted to be fed into the vane rear end through the pressure difference so that the rotation sliding operation may be effected with the vane being in contact at its tip end against the cylinder inner wall through the rotation of the rotor.
One example of a vane backpressure providing apparatus for the above-described conventional sliding vane type compressor will be described hereinafter with reference to the drawings.
FIG. 1 through FIG. 3 show the concrete construction of a sliding vane type compressor having the conventional differential pressure oil-feeding type vane backpressure providing apparatus. In the drawings, the vane backpressure providing apparatus for a sliding vane type compressor includes a cylinder 1 having a cylindrical inner wall, a rotor 2 for forming micro-gap in one portion of its outer periphery with respect to the inner wall of the cylinder 1, a plurality of vane slots 3 disposed in the rotor 2, a plurality of vanes 4 slidably inserted into the vane slot 4, a driving shaft 5 which is formed integrally with the rotor 2 and rotatably supported through an unnumbered shaft, a front side plate 6 and a rear side plate 7 which respectively blockade both the ends of the cylinder 1 to form a working chamber 8 inside, an inlet opening 9 communicating with the working chamber 8 on the side of the low pressure, a discharge opening 10 communicating with the working chamber 8 on the side of the high pressure, a discharge valve 11 arranged in the discharge opening 10, a high-pressure case 12 which forms a high-pressure chamber 14 communicating with the high-pressure passage 13 and has a screen 15 arranged to separate, catch the lubricating oil in the compressed high-pressure fluid, a vane backpressure providing apparatus main-body 16 disposed on the rear side plate 7 to feed into the vane backpressure chamber 17 the lubricating oil of the lower oil storing portion of the high-pressure chamber 14, an oil supply passage 18 for causing the lower oil-storing portion of the high-pressure chamber 14 to communicate with the vane backpressure chamber 17, a passage 19 for restricting the oil supply amount to be caused through the differential pressure, a first spherical seat 20 provided on the way to the oil-supply passage 18, a first spherical body 21 which is isolated from the first spherical seat 20 or comes into contact against it to cause the oil-supply passage 18 to communicate or to shut it off, a first plunger chamber 22 which opens to the first spherical seat 20 on the side opposite to the first spherical body 21, a first plunger 23 which is arranged slidably within the first plunger chamber 22 to isolate the first spherical body 21 from the first spherical seat 20 when it has been moved onto the side of the first spherical seat 20, a first pressure introducing passage 24 which causes the first lower plunger chamber 25 at the lower end of the plunger to communicate with the working chamber 8 located immediately before the discharge valve 11.
The vane backpressure providing apparatus for a sliding vane type compressor of the above-described construction will be described hereinafter in its operation.
When the driving shaft 5 and the rotor 2 are rotated clockwise in FIG. 2 through the reception of the power transfer from the driving source such as engine or the like, the low-pressure fluid flows into the working chamber 8 from the inlet opening 9. The high-pressure fluid compressed through the rotation of the rotor 2 lifts the discharge valve 11 from the discharge opening 10 to flow into the high-pressure chamber 14 from the high-pressure passage 13, so that the lubricating oil is separated and caught by the screen 15. On the other hand, the excessively compressed gas within the working chamber 8 having the pressure high enough to overcome the pressure of the high-pressure fluid to lift the discharge valve 11 is supplied to the first lower plunger chamber 25 from the first pressure introducing passage 24, and the first plunger 23 moves onto the side of the first spherical seat 20 to isolate the first spherical body 21 from the first spherical seat 20. Accordingly, as the oil supply passage 18 communicates, the lubricating oil which is separated from the high-pressure fluid and is stored in the lower high-pressure chamber 14 is fed into the vane backpressure chamber 17 from the passage 19 and the oil supply passage 18 by the differential pressure to serve for movement of the vane 4. It passes through the gap between the rotor 2 and the front side plate 6 or the rear side plate 7 to flow into the working chamber 8. Also, when the compressor has stopped, the pressure within the working chamber 8 rapidly drops down to the pressure of the fluid on the side of the low pressure, so that the pressure within the first lower plunger chamber 25 also drops down to the pressure of the fluid on the side of the low pressure, the pressure at the lower end of the first plunger 23 becomes smaller than the pressure at the upper end of the first plunger 23. Thus, the first plunger 23 moves onto the side of the first lower plunger chamber 25. The first spherical body 21 comes into the contact against the first spherical seat 20 to shut the oil-supply passage 18. As the lubricating oil is not supplied further, the liquid compression at the start of the compressor, which is caused by the lubricating-oil stay within the working chamber 8, may be prevented from being caused.
However, in such a conventional vane backpressure providing apparatus as described hereinabove, when the compressor starts in a state where the pressure of the fluid on the side of the low pressure has become equal to that of the fluid on the side of the high pressure after the lapse of a certain time after the stopping of the compressor, the vane rotates through the rotation of the rotor to try to extend from/retract within the vane slot. However, as the differential pressure for supplying the lubricating oil does not exist, and the resistance at the flow start through the fluid head, viscosity and inertia of the lubricating oil is large, the large amount of lubricating oil cannot be fed with respect to the volume variation in the vane backpressure chamber to be caused during the extension/retraction of the vane. Therefore, especially when the number of rotations is small at the start of the compressor, pressure reduction of the vane backpressure chamber is caused. The known failure phenomenon where the vane is isolated from the cylinder inner wall and comes into contact against it again or an inferior compression phenomenon where the fluid is not compressed is caused.
Also, to expand the passage area of the passage for retaining the lubricating oil amount depresses the vane excessively against the cylinder inner wall during the steady operation to cause friction increase in the vane tip end portion and the cylinder inner wall, and the input increase of the compressor so as to deteriorate the durability and efficiency of the compressor. The increasing centrifugal force of the vane increases this tendency further during the high rotation.